Congestive heart failure (“CHF”) is a condition typically caused by a structural or functional disorder of the heart and can impair the ability of the heart to fill itself or pump a sufficient amount of blood throughout a body (e.g., kidneys). It has been established in animal models that a heart failure condition can cause abnormally high sympathetic activation of the kidneys, which leads to decreased removal of water from the body, decreased removal of sodium, and increased secretion of renin. Increased renin secretion leads to vasoconstriction of blood vessels supplying the kidneys, which causes decreased renal blood flow. As a result, the reaction of the kidneys to heart failure can perpetuate a downward spiral of the heart failure condition. In addition, the kidneys also play a significant role in the progression of Chronic Renal Failure (“CRF”), End-Stage Renal Disease (“ESRD”), hypertension (pathologically high blood pressure), and other renal or cardio-renal diseases.
Reduction of sympathetic renal nerve activity (e.g., via denervation), can reverse these processes. Ardian, Inc. has developed methods and systems for treating renal disorders by applying an electric field to neural fibers that contribute to renal function. See, for example, Ardian, Inc.'s co-owned and co-pending U.S. patent application (a) Ser. No. 11/129,765, filed on May 13, 2005, (b) Ser. No. 11/189,563, filed on Jul. 25, 2005, and (c) Ser. No. 11/363,867, filed Feb. 27, 2006, all of which are incorporated herein by reference in their entireties. An electric field can initiate renal neuromodulation via denervation caused by irreversible electroporation, electrofusion, apoptosis, necrosis, ablation, thermal alteration, alteration of gene expression or another suitable modality. The electric field can be delivered from an apparatus positioned intravascularly, extravascularly, intra-to-extravascularly, or a combination thereof. Additional methods and apparatus for achieving renal neuromodulation via localized drug delivery (e.g., by a drug pump or infusion catheter), the use of a stimulation electric field, and other modalities are described, for example, in co-owned U.S. Pat. Nos. 7,162,303 and 6,978,174, both of which are incorporated herein by reference in their entireties.
Although these applications provide promising methods and systems, several improvements for enhancing the implementation of these methods and systems would be desirable.